Air bag system for automotive passenger seat

ABSTRACT

An air bag system for protecting a passenger seated on the front passenger seat of a vehicle. In an initial stage, the air bag is inflated mildly. In the subsequent stage, the bag is inflated also mildly. The directivity of produced gas can be reduced. The air bag can be inflated mildly while maintaining a large area. The air bag system comprises an air bag case having an opening on its top side, an inflator disposed inside the air bag case, the aforementioned air bag folded in the air bag case, and a diffuser mounted between the inflator and the opening in the case. The air bag is placed in a side-by-side relation to the inflator and located behind the inflator inside the case. The diffuser is provided with numerous holes for supplying the gas. The diffuser acts to regulate flow of the gas from the inflator. At least when the gas is produced from the inflator, a space is created between the outer surface of the inflator and the diffuser.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an air bag system for anautomotive front passenger seat and, more particularly, to an air bagsystem which detects a certain level of impact on collision of theautomobile and causes a gas to be produced from an inflator that is agas generator so as to inflate an air bag, thus constraining a passengerseated on the front passenger seat.

[0002] One kind of an air bag system for an automotive front passengerseat is a vertical type air bag system comprising an air bag case, aninflator mounted under the bag case, and an air bag mounted above it. Ina lateral type air bag system, an inflator is located on one side in anair bag case. An air bag and the inflator are arranged side by side in adirection parallel to the plane of the opening in the air bag case.Various lateral type air bag systems including this kind have beenproposed. These proposed systems are discussed in detail below.

[0003] One kind of lateral type air bag system has been devised by thepresent applicant and is described in Japanese Patent Laid-Open No.191362/1994. This system has an air bag case which opens to asubstantially horizontal surface of an automotive instrument panel. Aninflator and a zigzag folded air bag are mounted inside the air bag casesuch that the inflator is positioned ahead of the bag, i.e., theinflator is located closer to the front of the vehicle. An unfolded flatbag portion extends over the inflator. The inflator is provided with gassupport ports which are located at a front upper position and a rearlower position, respectively, in a horizontal cross section of theinflator.

[0004] In the operation of this air bag system, when a gas is producedfrom the inflator, the unfolded flat bag portion which is locatedimmediately above the inflator begins to inflate. Therefore, the upperportion of the bag expands upward first and swells into the spacedefined by the windshield extending obliquely and also by the instrumentpanel. As a result, the upper portion of the air bag assumes a givenshape. Subsequently, the lower portion of the air bag expands.Consequently, the whole bag expands into a desired three-dimensionalshape.

[0005] An example of a method for folding an air bag is seen in an airbag system described in Japanese Patent Laid-Open No. 227353/1994, alsoinvented by the present applicant. An embodiment of this air bag systemis similar in structure to the air bag system described in theabove-cited Japanese Patent Laid-Open No. 191362/1994 except that an airbag disposed in a side-by-side relation to an inflator inside an air bagcase has an upper, zigzag folded portion adjacent to the inflator and alower portion which is adjacent to the upper portion and wound into aroll. When the gas is produced from the inflator, the zigzag foldedportion loosens more easily than the lower wound portion. By making useof this fact, the upper portion of the air bag expands first when thegas is produced from the inflator. Subsequently, the lower portionexpands. As a result, the whole structure swells into a desiredthree-dimensional shape.

[0006] These well-known techniques control the behavior of expansion ofan air bag, by taking notice of the structure of a module.

[0007] In U.S. Pat. No. 5,405,164 (Japanese Utility Model No. 3014497),a diffuser is located over an inflator with a space between them. Thisinflator is shaped like a bottle. A gas is ejected from around a portformed at one side of the inflator. This is a so-called hybrid inflator.Since the gas injection portion is distributed unevenly in this way, thediffuser is mounted to regulate the flow of the gas from the port.Specifically, the diffuser is provided with minute holes in positionscorresponding to the opening in the inflator. The diameter of the holesincreases away from the opening.

[0008] Japanese Patent Publication No. 78052/1994 (U.S. Pat. No.4,998,751) discloses a technique for causing an inflator to exhibit anS-shaped output characteristic curve. In particular, this publicationsays, “It is an object of the present invention to provide an improvedtwo-chamber expansion system for imparting an S-shaped pressure-timeperformance curve to an air bag which protects an automotive passenger.In this expansion system, charges of a gas-generating agent in thechambers are simultaneously ignited by a single blasting device. It is amore specific object of the present invention to provide a two-chamberexpansion system which delays ignition of the gas-generating agent inthe second chamber after the gas-generating agent in the first chamberis ignited, the expansion system being further characterized in that theduration of the delay is achieved by the structure and shape of theblasting device.” (column 7, lines 9-17). This system is capable ofexpanding the air bag slowly at first to mildly push the passenger if heor she is a child assuming an inappropriate posture. Then, a controlled,released gas is supplied into the air bag so as to expand the bagquickly to protect the seated passenger, irrespective of his or herbuild (column 17, lines 34-38). The output characteristic curve isshaped into an S-shaped form by adopting this inflator. That is, theoutput of the inflator can be made low at first. However, the effect ofthe S-shaped characteristic curve may be lessened, depending on thestructure of the module located downstream of the inflator as viewedfrom the injected gas stream. Furthermore, the bag is not expandedmildly throughout the process of expansion.

[0009] These air bag systems control the behavior of expansion of airbags, by taking notice of only the inflator output and the regulationprovided by the diffuser.

SUMMARY OF THE INVENTION

[0010] It is a first object of the present invention to provide an airbag system which inflates an air bag mildly during its initial phase ofexpansion by finding a correlation between the inflator outputcharacteristic and a modular structure. It is a second object of theinvention to permit the air bag to be inflated mildly during all phasesof the inflation of the air bag.

[0011] The present invention is intended to achieve these objects. Anair bag system is provided that includes an air bag case having anopening on a top side, an inflator disposed inside the air bag case, afolded air bag juxtaposed to the inflator and disposed behind theinflator inside the air bag case (i.e., the air bag is located closer tothe rear of the vehicle than the inflator), and a diffuser forregulating a stream of a gas from the inflator. The diffuser is locatedbetween the inflator and the opening in the air bag case, and isprovided with a plurality of gas supply nozzles or holes. A space iscreated between the outer surface of the inflator and the diffuser atleast when the gas is produced from the inflator.

[0012] The diffuser may be made of a metal or other rigid substance.Furthermore, the diffuser may be made of cloth or other soft material.In the latter case, when the air bag has been folded, the diffuser is inintimate contact with the outer surface of the inflator. However, whenthe gas is being produced from the inflator, the diffuser is alsoinflated, thus creating the space between the diffuser and the inflator.

[0013] Since this air bag system is equipped with the diffuser, the gasspouted from the inflator is temporarily stored in the space between theinflator and the diffuser. The stored gas is mildly supplied as aregulated stream from openings in the diffuser into the air bag. Forthis purpose, the space between the inflator and the diffuser preferablyhas a volume adapted to temporarily store the gas produced from theinflator. Furthermore, it is desired to appropriately determine thenumber of the holes, or openings, in the diffuser, the total area of theholes, and their positional relationship. The amount of the gasexhausted is made uniform over the whole outer surface of the diffuser.

[0014] In another feature of this air bag system, the inflator and theair bag are arranged side by side. Consequently, the upper portion ofthe air bag is inflated first. Then, the lower portion is inflated.Hence, mild expansion is accomplished.

[0015] The air bag disposed in the air bag system has a folded portionwhich can comprise an upper zigzag folded portion and a lower portionwound into a roll. The upper portion is adjacent to the inflator. Thelower portion is adjacent to the upper portion. In this structure, whena gas is supplied into the air bag, the upper zigzag portion of the airbag inflates first. Then, the lower coiled portion inflates. As aconsequence, milder expansion of the whole air bag is achieved.

[0016] This air bag system can be of a so-called top-mounted type. Inthis case, the opening in the air bag case lies in a substantiallyhorizontal surface of an instrument panel. Accordingly, the gas meetsthe surface of the flat portion located over the inflator, i.e., theunfolded portion, and this portion first inflates. Then, this flatportion and the following upper portion of the folded portion swell intoa space defined by a windshield and the instrument panel. As a result, adesired two-dimensional spread is obtained. Subsequently, the followinglower portion of the folded portion swells in such a way as to growdownwards from the upper portion of the air bag inflated in twodimensions. Consequently, the air bag inflates into the desiredthree-dimensional shape.

[0017] Let Q_(t) be the total amount of gas produced during a timeinterval between 0 and t msec. Let A be the cross-sectional area of theopening in the air bag case. In this air bag system, the ratio Q_(t)/Apreferably varies in several stages as given below.  0 msec Q₀ /A = 0l/cm₂  5 msec Q₅ /A ≦ 0.107 l/cm₂ 10 msec Q₁₀ /A ≦ 0.215 l/cm₂ 20 msecQ₂₀ /A ≦ 0.537 l/cm₂ 30 msec Q₃₀ /A ≦ 0.934 l/cm₂

[0018] This makes it possible to inflate the whole air bag mildly. Inthe above relations, the total amount Q_(t) of the produced gas is anapparent volume depending on the number of moles produced and amount ofheat.

[0019] In this air bag system, the inflator may have two or more squibs(electric detonators). In this case, a delay time can be introduced inthe ignition time, and the output can be adjusted. More specifically,generation of the gas from the inflator is carried out in two stages. Asa consequence, the whole air bag is inflated more mildly. In addition,the inflator may also be a hybrid inflator having the two or more squibsas described above and two or more associated gas generators eachcontaining an explosive charge and a gas-generating agent. Thus, theinflator is charged with a compressed gas.

[0020] Generally, it is advantageous for this air bag system to use aso-called hybrid inflator. Normally, heat is utilized to expand a gas.Inflators are broadly classified into two major categories:pyrotechnique inflator and hybrid inflator. The former makes use ofpyrotechnics, i.e., explosive charges. Typical examples are described inthe above-cited Japanese Patent Publication No. 78052/1994, in which anS-shaped curve is achieved with a pyrotechnique inflator. The latterconsists of a bottle-like container mainly charged with a pressurizedgas and a gas propellant, and is cited in the abovementioned U.S. Pat.No. 5,405,164. Specifically, a squib is mounted in the opening at oneend of the bottle-like container. The squib is excited by an electricalsignal. Then, a sagittal member disposed adjacent to the squib is movedaxially through the container. This breaks a pressure partition thatisolates the pressurized gas from the outside atmosphere. Then, thepressurized gas is produced through the opening and supplied into theair bag. The sagittal member also acts on the explosive charge. Theresult is that the gas-generating agent placed around the explosivecharge is reacted, thus giving heat to the pressurized gas. Theexpansion of the gas is promoted further. In this way, the hybridinflator is little assisted by heat during an initial phase ofgeneration of the gas. This initial phase corresponds to the initialphase of the expansion of the air bag. Therefore, the outputcharacteristic of the hybrid inflator produced during this time intervalis more easily adjusted mechanically and dimensionally than thepyrotechnique inflator which depends chiefly on a chemical reaction.

[0021] On the other hand, where the diffuser is adjusted to adjust thegas finally entering the air bag, it is necessary to adjust the volumeof the space between the inflator and the diffuser. However, thisapproach has limitations, since a space accommodating the bag must besecured. Furthermore, the total area of the nozzles or holes, theirarrangement, and other factors must be adjusted. In this way, variouslimitations exist. Accordingly, it is desired to adopt a hybrid inflatorwhose output is easily matched to these limitations.

[0022] Other objects and features of the invention will appear in thecourse of the description thereof, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a cross-sectional view of an air bag system according tothe present invention in an assembled state taken along line I-I of FIG.2;

[0024]FIG. 2 is an exploded perspective view of the air bag system shownin FIG. 1;

[0025]FIG. 3 is a cross-sectional view taken on line III-III of FIG. 2of the air bag system in an assembled state;

[0026]FIG. 4 is a view similar to FIG. 1, but showing another embodimentof the air bag system according to the invention;

[0027]FIG. 5 is a view similar to FIG. 1, but showing a furtherembodiment of the air bag system according to the invention;

[0028]FIG. 6 is a view similar to FIG. 1, but showing a still otherembodiment of the air bag system according to the invention;

[0029]FIG. 7 is a view similar to FIG. 1, but showing a yet otherembodiment of the air bag system according to the invention; and

[0030]FIG. 8 shows a schematic of an inflator.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Referring to FIGS. 1-3, there is shown an air bag systemaccording to the present invention. The air bag system is used for apassenger seated on a front passenger seat of a vehicle. The system islocated under the instrument panel (not shown) which is substantiallyhorizontal. The system has an opening located immediately under theinstrument panel. Indicated by W is the windshield, or front window, ofthe vehicle.

[0032] This system comprises a hybrid inflator 1, an air bag 2 inflatedby a gas from the inflator 1, and an air bag case 3 accommodating bothinflator 1 and air bag 2. The inflator 1 consists of a bottle havingholes 1 a in its neck. The case 3 is open at its top side. Inparticular, inside the air bag case 3, the inflator 1 is located on aside F of the front of the vehicle. The folded air bag 2 is located on aside R of the rear of the vehicle. That is, the bag 2 is positionedbehind the inflator 1. A diffuser 4 is mounted between the inflator 1and an interior of the air bag 2 to regulate flow of the gas from theinflator 1.

[0033] Since a position at which a top side of fringes 2 b of an openingin the air bag is ahead of the inflator 1, cloth on a top portion of theair bag 2 bridges across the inflator 1. A folded portion of the air bag2 is located behind the air bag 2. Therefore, the top portion of the airbag 2 can be first unfolded during operation.

[0034] In the air bag system, the diffuser 4 and a wall portion 3 a ofthe air bag case 3 together form a space 5 around the inflator 1.Extensions are formed at ends of the diffuser 4 to form retainers 6which squeeze the fringes 2 b of the opening in the air bag 2 againstthe air bag case 3. Since the retainers 6 and the diffuser 4 are formedintegrally in this way, the system is made up of a fewer number ofcomponents than conventional. Also, the system can be manufactured witha fewer number of steps. In addition, the air bag 2 is quite easy tomount.

[0035] A bolt 1 b is mounted to a foot of the inflator 1, extendsthrough the air bag case 3, and is fixed with a nut 7. The inflator gasis ejected from holes 1 a which are distributed unevenly. The ejectedgas is regulated by holes 4 a in the diffuser 4, as shown in FIG. 3, andis supplied into the air bag 2. The diffuser 4 is a curved regulatorplate and covers the outer surface of the inflator 1 mounted in the airbag case 3 with the given space 5 left around the inflator 1. Dependingon the positional relation of the diffuser 4 to the inflator 1, thediffuser 4 may be flat. The holes 4 a formed in the surface of thediffuser 4 are distributed in a given manner to supply the gas streaminto the air bag 2 uniformly. The gas released from the inflator is oncestopped and stored in this space. Then, the regulated gas stream ismildly supplied from the surface of the diffuser 4 into the air bag 2.The flow rate of the gas supplied into the air bag 2 is varied inseveral stages, by adjusting the volume of the space 5, the number ofthe holes 1 a, and a total area of the holes 4 a while maintaining abalance with the output characteristic of the inflator. The air bag 2 ismildly inflated during its initial phase of expansion. The air bag 2 isinflated also mildly during the subsequent phase. Generally, withrespect to the holes 4 a in the diffuser 4, many smaller holes arepositioned close to the holes 1 a in the inflator 1 and comparativelylarge fewer holes are located remotely from the inflator holes 1 a. Thisstructure is desirable for regulation of the gas supplied into the airbag 2.

[0036] The inflator 1 is cylindrical in shape. In this inflator 1, thegas-generating agent is ignited. The resulting pressure and heat releasethe pressurized gas from the container. The inflator 1 is a so-calledhybrid inflator.

[0037] As described above, the air bag opening that is an inlet port forintroducing the gas into the air bag 2 may be fixed to the air bag caseopening. Instead, the opening may be wound around the inflator as shownin FIG. 5. The air bag 2 in FIG. 5 is otherwise folded in a manner asshown in FIG. 1. That is, each folded portion extends substantiallyhorizontally. Referring again to FIGS. 1-3, an upper portion of the airbag 2 is folded in a zigzag fashion. A following lower portion is woundinto a roll, a wound portion a, and is received on the bottom of the airbag case 3. The zigzag folded portion b is received near the opening inthe air bag case 3. The zigzag folded portion b terminates in a flat,unfolded portion c which is close to the opening in the air bag 2. Theportion c bridges over the inflator 1. The upper side of the fringe 2 bof the opening in the air bag 2 is held between the retainers 6 and 6′mounted to a front wall of the air bag case 2 and the inflator,respectively. Since the air bag 2 is folded and wound in this way, theflat portion c is first unfolded obliquely upwardly and rearwardly alongthe windshield W. These portions are unfolded in this order. Since theseportions are successively inflated in this manner, mild expansion isaccomplished throughout the whole inflation process.

[0038] With respect to the contour of the opening in the air bag case 3,the dimension taken longitudinally of the vehicle is preferably inexcess of 120 mm, and the dimension taken across the vehicle ispreferably in excess of 190 mm. In this case, the area A of the openingin the air bag case 3 is greater than 228 cm². It is desired to set thedepth of the case, or dimension taken vertically of the vehicle, toabout 100 mm, taking account of the diameter of the inflator, the spaceaccommodating the air bag 2, and the volume of the folded air bag 2.

[0039] In this system, the generated gas which is supplied from theopening in the air bag case 3 into the air bag 2 through the diffuser 4expands according to the number of moles and amount of heat. The amountof gas passing through the opening in the air bag case 3 divided by thecross-sectional area of the air bag case 3, i.e., Q_(t)/A where Q_(t) isthe total amount of gas produced during a time interval from 0 to tmsec, and A (A≧228 cm²) is the area of the opening in the air bag case3, varies with time in several stages as follows:  0 msec Q0 / A = 0l/cm²  5 msec Q5 / A ≦ 0.107 l/cm² 10 msec Q10 / A ≦ 0.215 l/cm² 20 msecQ20 / A ≦ 0537 l/cm² 30 msec Q30 / A ≦ 0.934 l/cm²

[0040] In this way, in the above-described embodiment, the gas issupplied mildly. The gas is supplied into the upper portion of the airbag 2 to inflate the upper portion first. Then, the lower portion isexpanded. Therefore, during its initial phase of the expansion, the airbag 2 is inflated in several phases over the instrument panel whilemaintaining the wide area of the inflated air bag efficiently. The airbag 2 inflates so as to surround the instrument panel. The extent ofexpansion is made large efficiently. The whole air bag 2 can be inflatedgradually with a large area. Therefore, the directivity of the expansionof the air bag 2 is reduced. This permits the air bag 2 to inflatemildly.

[0041] The system may also incorporate a module using an inflator 1having two squibs 60 as shown in FIG. 8. A delay time is introduced inthe ignition time to adjust the output.

[0042] Referring next to FIG. 4, there is shown another embodiment ofthe invention. Like parts are indicated by like reference numerals inthe embodiment of FIGS. 1-3 and also in the embodiment of FIG. 4, butnumeral 10 is added to the numerals used in FIG. 4.

[0043] In this embodiment, an air bag case 13 assumes a boxlike shape. Adiffuser 14 of a cross section consisting of about three quarters of acircle is mounted around an inflator 11 with a space 15 between them. Anair bag 2 is composed of an upper portion b and a lower portion a. Whenthe air bag 2 is folded, the upper portion b is folded in a zigzagfashion and the lower portion a is wound into a roll, in the same way asin the case of FIG. 1. A flat, unfolded portion c exists near theopening in the case 13. At one end of the flat portion c, i.e., theupper side of the fringe 2 b of the opening in the air bag 2, is securedwith a bolt and a nut to an upper end of a left side wall of the case 13as viewed in the figure. The lower side of the fringe 2 b of the openingin the air bag 2 is similarly anchored to an upper side of a right sidewall of the case 13.

[0044] An embodiment shown in FIG. 5 is similar to the embodiment ofFIG. 4. In FIG. 5, the like reference numerals to which 10 is added arereplaced by the like reference numerals to which 20 is added. Thisembodiment is characterized in that an air bag 22 is provided with noopening. An inflator 21 and a surrounding diffuser 24 are disposedinside the air bag 22. The inflator 21 and the diffuser 24 are fastenedto the air bag case 23 by means (not shown).

[0045] Referring to FIG. 6, there is shown a still other embodiment ofthe invention. In FIG. 6, those parts which correspond to like parts ofthe embodiment of FIG. 1 are indicated by like reference numerals towhich 30 is added. This embodiment is characterized in that an air bag32 is folded not horizontally but vertically, unlike the aboveembodiments. An air bag portion b′ adjacent to an inflator 33 is foldedin a zigzag manner, and an adjacent portion a is wound into a roll. Anair bag portion c extending from the portion of the folded portion b′closest to the inflator 33 to the upper side of the fringe in theopening in the air bag is not folded but kept flat.

[0046] The air bag 32 is disposed in a side-by-side relation to theinflator inside the air bag case. The manner in which the air bag 32 isfolded and wound is not limited to the foregoing method. As shown inFIG. 7, the whole air bag 42 can be folded in a zigzag manner asindicated by b. Furthermore, the whole air bag 42 may be wound into aroll (not shown). The air bag case has a door D.

[0047] In the present invention, an air bag is inflated mildly in aninitial stage. This makes the subsequent expansion milder. Furthermore,the directivity of the gas can be diminished. Therefore, the air bag canbe expanded into a desired shape mildly while maintaining a large area.

1. An air bag system for use in a vehicle, comprising: an air bag casehaving an opening on its top side; an inflator disposed inside said airbag case and having an outer surface; a folded air bag arranged in aside-by-side relation to said inflator and located behind said inflatorinside said air bag case; a diffuser mounted between said inflator andsaid opening in said air bag case and provided with a plurality of gassupply holes, said diffuser acting to regulate flow of a gas from saidinflator; and a space created between the outer surface of said inflatorand said diffuser at least when the gas is produced from said inflator.